The purpose of this project is to determine the neuropsychological deficits most characteristics of patients in the earliest stages of Alzheimer's disease (AD) or who are at risk for AD. A secondary but related aim is to determine whether the rate or pattern of cognitive decline differs as a function of the age of disease onset. Since the two greatest risk factors for AD are old age and familial aggregation two groups at increased risk for AD are the very old and first degree relatives of AD patients. Both groups are available for this project. Patients in the following groups will be evaluated every six months: cognitively normal elderly, elderly persons with cognitive decline but who do not meet NINCDS criteria for AD, early AD, AD, first degree relatives of AD patients. Serial tests will assess aspects of memory, language, praxis, psychomotor speed, and verbal I.Q. It is hypothesized that delayed recall memory tests and measures of psychomotor speed will best differentiate early AD and high risk persons and their discriminating power may be greater when corrected for verbal I.Q. All participants except the first degree relatives will be enrolled in an autopsy program and will provide neuropathologic and neurochemical data for correlative studies. Acute phase reactants, a potential biologic marker of early AD will be measured in all groups and will be available for correlative studies.